The proposed study will examine and compare the specificity, kinetics and inhibition of estrogen sulfotransferases of endocrine (bovine adrenal) and non-endocrine (bovine hepatic) origin. The enzymes will be isolated by ammonium sulfate fractionation, gel filtration and preparative gel electrophoresis, and specific site-directed, irreversible inhibitors of sulfation of steroids will be designed. The application of such inhibitors should contribute to the understanding of the role of sulfation of steroid hormones, in general, and of the role of sulfation and metabolism of estrogen hormones in human breast tumors, in particular.